This invention relates to electrostatographic imaging systems. More specifically, the present invention is directed toward a power supply for regulating the charging currents for a plurality of corotrons in an electrostatographic system.
The currents generated by corotrons in electrostatographic systems have been regulated by various feedback techniques. Typically, the shield current, the plate current, or a grid current in the case of a scorotron, is detected and used to develop an error signal. The error signal is fed back to the power supply to increase or decrease the input voltage or current to compensate for the detected error. The reason for the regulation is to correct for changes in the ambient conditions of temperature and humidity, for coronode wire to plate spacing and for changes in capacitance such as that due to transfer paper thickness variations or photoconductor, i.e., the plate, thicknesses variations. In other words, the regulation of corotron current is to compensate for current fluctuations under changing load conditions.
The prior art electrostatographic imaging systems, specifically electrophotographic imaging systems, often choose to ignore the load variation to a particular corotron and do not provide any feedback regulation. When regulation is provided, it is most commonly applied to the charging corotron since its function is extremely important. It is known to have the charging corotron regulated and the transfer, detack and erasing or leveling corotrons operated in open loop. It is most common for all the corotrons to be operated in open loop.
Input line voltage regulation has been provided for corotrons by using a controlled voltage transformer, CVT. The input voltage coupled to the primary of a CVT can vary a significant amount without causing a change in the current in the secondary or output windings. This is an important feature in most applications since line voltage often varies as much as plus or minus ten percent. Nonetheless, the CVT does not provide regulation for the corotron due to changes in ambient and other load parameters.